Leah, who vanished Monday, appeared to have been strangled, the sources added, but said an autopsy will determine the official cause of death.

Walsh was charged after investigators grilled him throughout the day about the mysterious disappearance of Leah, whose car, with a flat tire, was found abandoned on the side of the Seaford-Oyster Bay Expressway.

A “help van” driver stopped to assist and reported seeing a man run from the abandoned car into a yellow car, the sources said; William’s vehicle is that color.

Leah’s body turned up less than 15 miles from her Bethpage home.

A worker at the nearby North Hills Country Club made the grim discovery about 50 feet off the Long Island Expressway’s westbound service road. The body had been there for more than 24 hours.

The couple had been fighting recently, and had a big blowup Saturday after he returned from a trip to Atlantic City and “went berserk on her,” said her college pal Lucas Bean.

While Leah and her husband, both 29, rode in a car that night, she secretly was sending Bean text messages from her cellphone.

“She told me the marriage is over. [She said,] ‘I’ll tell you why when I talk to you. It’s something really, really bad,’ ” said Bean, her classmate at the University of Massachusetts Amherst.

“[She said] she was definitely getting a divorce. There was no way she could stay with him after what he’d done. I never found out what it was [about].”

The couple had been married for three years.

The well-liked teacher had just received her master’s degree from Molloy College in Rockville Centre and taught autistic children.

A police source said she texted her husband the morning she vanished, and her cellphone has not been found.

William – who had been questioned on Tuesday as well – told reporters hours before his arrest that he was going to put up fliers to help find his wife.

A neighbor of Leah’s parents in Rockville Centre said the couple fought frequently when they lived there.

“I heard him being very abusive to her verbally, cursing,” said one neighbor, who asked not to be identified. “Cursing, ‘F- – – you!’ screaming at the top of his lungs and she was just very distraught.”